1. Field of the Invention
The present invention relates to a photo printer for forming an image on a roll paper by heating, and then fixing the image by applying a light having a predetermined wavelength.
2. Description of the Related Art
The photo printer forms a full color image by repeating a process of image formation by heating of a thermal head and image fixation by applying ultraviolet radiation, using a roll paper having a laminate of three thermally coloring layers that are colored in three primary colors of Y (yellow), M (magenta) and C (cyan).
Referring to FIG. 5, an image forming and fixing process for the conventional photo printer will be described below. FIG. 5 is a schematic view showing successively an image forming and fixing process for the conventional photo printer. Reference numeral 3 denotes an image forming portion, 4 denotes an image fixing portion, 23, 24 denote a pair of conveying rollers for conveying a roll paper 100, and 61, 62 denote a pair of delivery rollers for use to carry in or out the roll paper. The image forming portion 3 includes a thermal head 31 for forming a predetermined image on the roll paper 100 by heating and a conveying roller 32 disposed at a position opposed to the thermal head 31 via the roll paper 100. The image fixing portion 4 includes the magenta fixing (M fixation) fluorescent lamps 41a, 41b, a reflector 42 surrounding them from the lower and side faces, the yellow fixing (Y fixation) fluorescent lamps 43a, 43b, a reflector 44 surrounding them from the lower and side faces, a shutter 45 for intercepting lights (ultraviolet rays) from the magenta fluorescent lamps 41a, 41b or yellow fluorescent lamps 43a, 43b, and a guide 46 for reciprocating the shutter 45 in the conveying direction of the roll paper 100.
First of all, one end of the roll paper 100 is forwarded up to a predetermined position in a direction to the delivery roller pair 61, 62, and pulled back in a direction to the image forming portion 3. Herein, the thermal head 31 of the image forming portion 3 is preheated at a (low) temperature for forming the yellow image, and forms an image (Y image) at a predetermined position at the temperature for forming the yellow image, while pulling in the roll paper 100 (FIG. 5A).
Then, the roll paper 100 having yellow image formed is forwarded in the direction to the delivery roller pair 61, 62 again, and the shutter 45 is moved over the yellow fixing fluorescent lamps 43a, 43b and the reflector 44 (FIG. 5B). Herein, the roll paper 100 is stopped at a position where a trailing end of an area where the yellow image is formed (Y image formed area) coincides with the leading end of the shutter 45.
Then, the yellow fixing fluorescent lamps 43a, 43b are lighted, and the roll paper 100 is pulled into the image forming portion 3 at a predetermined speed. In this case, the shutter 45 is moved toward the image forming portion 3, while a positional relation between the trailing end of the Y image formed area on the roll paper 100 and the leading end of the shutter 45 is kept (FIG. 5C). Thereby, light is only applied to the yellow image formed area of the roll paper 100 to fix the yellow image (Y fixation). Herein, the shutter 45 is moved together with the roll paper 100, thereby preventing light from the yellow fluorescent lamps 43a, 43b from being directly applied to the area where no image is formed (Y unfixed area) following the trailing end of the yellow image formed area (Y image formed area).
Then, the yellow fixing fluorescent lamps 43a, 43b are turned off, and the roll paper 100 is forwarded to the delivery portion 6. At this point of time, the shutter 45 is moved above the yellow fluorescent lamps 43a, 43b to open an upper part of the magenta fluorescent lamps 41a, 41b. 
And the thermal head 31 is heated to a magenta image forming temperature (medium temperature), and performs an image formation (M image formation) in a predetermined area at the magenta image forming temperature, while pulling back the roll paper 100 (FIG. 5D).
Then, if the leading end of the roll paper 100 arrives to a predetermined position near an end portion of the reflector 42 on the side of the thermal head 31, the magenta fixing fluorescent lamps 41a, 41b are lighted, and the roll paper 100 is forwarded toward the delivery roller at a predetermined speed (FIG. 5E). If the trailing end of the magenta image forming area of the roll paper 100 arrives to the end portion of the reflector 42 on the side of the thermal head 3, the magenta fixing fluorescent lamps 41a, 41b are turned off (M fixation).
Thereafter, a cyan image is formed by the thermal head 31, though being not shown. Then, the roll paper 100 is forwarded to a predetermined position, cut into a predetermined size and carried out.
In a conventional image forming apparatus, a thermosensible recording medium of predetermined size is placed on the outer surface of a cylindrical drum provided internally with ultraviolet radiating lamps, and the image is formed from the outside by the thermal head and fixed with ultraviolet rays from the ultraviolet ray radiating lamps internally provided (refer to JP-A-5-104751).
However, in the photo printer as shown in FIG. 5, a yellow image fixing portion composed of the yellow fluorescent lamps and the reflector and a magenta image fixing portion composed of the magenta fluorescent lamps and the reflector are arranged in series in a roll paper conveying direction. Thereby, the outside dimension of the apparatus in this direction can not be reduced, depending on the size of two image fixing portions, especially the length size in the roll conveying direction. To radiate light evenly over the roll paper conveyed in a horizontal direction, a plurality of (two in FIG. 5) line light sources (fluorescent lamps) are needed. Furthermore, to prevent light radiated from the fluorescent lamps from being applied on an area of the roll paper where fixation is undesired, the shutter for intercepting light is linked. However, a mechanism for operating the shutter in accordance with a conveyance of the roll paper, for example, a combination of multiple gears and clutches, must be provided, making the structure more complex.
On the other hand, JP-A-5-104751 has a structure in which the thermosensible recording paper is pasted on the drum, whereby the cut paper of predetermined size is employed, and the roll paper can not be employed. The thermosensible recording paper must be replaced every time of printing, whereby the printing operation is very troublesome.